For more than a decade, spectral radiance data obtained from airborne and orbital platforms has been used to quantify the 3-dimensional special and temporal variability of atmospheric temperature and moisture fields, so as to understand and predict the development of extreme weather events. In particular, data from the Atmospheric Infra-Red Sounder (“AIRS”) on the NASA Aqua spacecraft have been routinely used for this purpose.
Assimilation of AIRS radiances in channels which support the derivation of high vertical resolution moisture and temperature field measurements and similar measurements, for example by the EUMETSAT/IASI (EUropean organisation for the exploitation of METeorological SATellites/Infrared Atmospheric Sounding Interferometer), have had a greater impact on the accuracy of medium-range numerical weather forecasts than that of any other single instrument. However, their LEO orbits (“Low Earth Orbits”) allows at most two observations per day per platform, which limits the ability to comprehensively sample rapidly changing atmospheric fields.
The NASA/NOAA GOES-R HES (“Geostationary Operational Environmental Satellite R-series Hyperspectral Environment Suite”) program sought to provide this high vertical resolution capability in geostationary orbit, which has been the traditional choice for high resolution temporal frequency measurements. However, HES has been deferred indefinitely following the formulation phase due to the expected high cost and high risk of cost growth in the development of a geosynchronous implementation. In particular, attaining finer spatial resolution observations of these atmospheric fields, for example resolutions in the range of 1-3 km, would be very challenging and costly to obtain from geosynchronous orbit.
In order to better understand the initiation and development of extreme weather events, the spatial resolution and temporal refresh rate of measurements of the atmospheric temperature and moisture fields and their dynamics must be substantially improved.
Numerous studies illustrating the substantial potential for weather forecast improvements due to rapidly refreshed high spectral resolution infrared spectral sounding measurements were performed in advance of, and during the GOES-R HES Formulation Phase. In general, these benefits are the result of comparative measurements that show the development of unstable atmospheric conditions or that reveal motion of the atmosphere at different altitudes.
Recent analysis by members of the NASA AIRS Science Team shows that observations in the spectral range 1950-2450 cm-1 at AIRS' spectral resolution, result in vertical temperature profile retrieval accuracy in the lower troposphere nearly as good as that derived using the full AIRS spectral channel set. FIG. 1A is a graph of AIRS/AMSU retrievals global cases for Jul. 10, 2012. It shows RMS differences from ECMWF “truth” of Quality Controlled (QC'd) AIRS/AMSU temperature profile retrievals obtained when using all AIRS channels and when using all but 15 μm or 11 μm AIRS bands. Results are shown using two QC procedures: data assimilation QC, which accepts fewer but more accurate retrievals, and climate QC, which accepts many more retrievals derived under more difficult cloud conditions. Results obtained using only mid-shortwave channels is somewhat degraded from those using all AIRS channels, but are still very good using either QC procedure. While these studies included concurrent use of AMSU observations, results obtained using all MWIR AIRS observations, but without using any AMSU observations, are similar.
Weather and climate processes are intimately linked by water vapor. Accurate knowledge of the distribution of water held in the atmosphere is therefore indispensable to predicting the amount, time, and location of precipitation. Recent studies by the National Research Council (NRC) and the Intergovernmental Panel on Climate Change (IPCC) showed that the Earth's climate can undergo changes in response to increasing concentrations of other greenhouse gases and aerosols, and that these changes may profoundly affect atmospheric water vapor, clouds, and precipitation patterns. Observation of changes in the distribution and dynamic behavior of water vapor in the coming years would further quantify the relationship between greenhouse gas concentrations and environmental phenomena with the greatest impact on human society, ranging from drought to severe storms, and would improve our ability to forecast the impact of these changes in the most policy-relevant terms. High-frequency measurements are especially important for characterizing these relationships and noting potential changes in dynamic weather events and/or diurnal convective processes. Recently, the assimilation of AIRS radiances into a regional atmospheric model has shown to improve the accuracy of precipitation likelihood predictions.
Cloud-resolving models under development today will likely form the basis for the next generation of weather and climate models. FIG. 2 shows improvements in GCM resolution compared to infrared and microwave observations over the past three decades. The trend line projects that operational models will be operating at horizontal spatial resolutions of 2-3 km within the next decade. Regional high resolution models are already being used operationally. Prior work also demonstrates that validation of a model of a given resolution must have observations as good as, or better than, the model itself, in order to minimize errors due to Nyquist spatial filtering processes in the models.
Unfortunately, the horizontal resolutions of current IASI and JPSS systems are coarser than 10 km, and the horizontal resolutions of the microwave and GPS-RO soundings are many 10's of km.
The societal value of fundamental measurements of the atmosphere, including the vertical temperature and moisture profiles and related characteristics, have long been recognized (See GOES-R HES discussion and Weather Panel Report Section) for their value in ongoing fundamental research, for the supporting data they provide for new research missions, and their value for operational earth observations for weather forecasting and other applications. However, the large programmatic failures of NPOESS and large disruptions to the GOES-R program are traceable in part to the spiraling complexity and cost associated with development of large instruments and multi-payload platforms such as NPOESS and GOES-R. NASA and other space agencies are exploring the use of distributed observing system architectures for various environmental observations.
The driving technical challenges on this path arise from the need to provide observations of the required data quality while fitting within the severe payload accommodation constraints of an economically favorable distributed architecture. Unfortunately, high spectral resolution payloads are typically large, heavy, and complex, and require large amounts of electrical power, especially for cooling. As a consequence, such instrument systems are expensive, and difficult to accommodate on space and airborne platforms, limiting their use.
A need, therefore, exists for a smaller, lighter, less complex, more energy efficient system for high spatial and temporal resolution measurement of atmospheric temperatures and moisture fields and their dynamics.